How to Get a Breast Pump Flange that Fits
Finding the right size of breast pump flange can make a huge difference in how comfortable—and effective—pumping is. If you’ve been using the flange size that came with your pump, there’s a good chance it’s not the best fit for your body.
Let's change that.
In this guide, I’ll show you how to measure your nipple using a flange ruler, share a breast pump flange size chart, and help you figure out exactly which flange size will work best for you.
Understanding Pump Flange Sizing
Have you been wondering how to know what size flange you need for your breast pump? It’s no wonder. The size of breast pump flange that comes with most pumps is based on outdated advice. Most pumps still come with a standard 24mm or 28mm breast pump flange size.
Logically, you’d think one of those sizes would be the right fit—because surely a pump wouldn’t come with flanges that don’t work for most people, right?
Unfortunately, that’s exactly what happens. There hasn’t been much actual research into pump sizing, and for a long time, the people designing breast pumps weren’t folks who had ever pumped.
Traditionally, the instructions that come with your pump suggest adding 4-5mm to your nipple size and picking one of their two standard options. But more recently, lactation professionals have started experimenting with smaller flange sizes—and the results have been consistently good. And here’s an actual study to back that up.
What this study (and good old common sense) found is that every body is different. The best size breast pump flange for you is the one that works best for your body—and it’s often a lot smaller than your pump instructions suggest.
While picking your best pump flange size might seem simple, there are a few important steps to take to get your ideal fit.
Measuring Your Body
The very first thing you need to do to determine your perfect flange fit is to measure your nipples. There is no average flange size that works for everyone, because your anatomy isn’t like anyone else’s nipple.
Measuring is easy—you can either use a flange size ruler printable PDF or you can purchase a metric ruler online—you want something with ranges between 10mm and 24mm. Or you can download mine for free below.
Alternatively, you can use digital calipers or an engineering ruler that has circles with sizes 10-24mm.
Print Your Flange Ruler
When printing a guide, make sure your print settings are set to 100%, and always double-check the size to make sure it’s accurate before you measure your nipples.
If you have a ruler with metric units, you can just measure the diameter of one of the circles to make sure it matches exactly. If you don’t have a metric ruler and yours only shows inches, no problem—my guide includes a 1” box at the bottom to check the scale. If that box measures exactly one inch, the circles are the right size too.
Measure Your Nipple Size
Once you have your ruler, it’s time to measure. You want to measure the base of your nipple, right where it connects to your areola.
If you’ve downloaded my guide, you’ll need to cut out the holes and use those to measure your nipples. I made the holes blue so it’s easy to see if you’ve cut everything out. You won’t need to cut out every hole—just eyeball the ones you think are closest to your nipple size, and cut out 3-4 circles as carefully as you can to make sure you get the snuggest fit.
The correct size is the smallest hole that comfortably slides all the way down to the base of your nipple.
If you’re using digital calipers instead of the flange ruler, lightly rest the tool around your nipple without compressing it. Write down the nipple measurement you find—this will be your starting size for a better flange fit.
Make sure you measure both sides. Our bodies aren’t always symmetric, and you want to make sure you get the right fit everywhere.
Here is a video to help you print and measure your nipple if this process feels confusing:
Find Your Breast Pump Flange Size
While printing your chart and measuring your nipples with the flange ruler was pretty straightforward, figuring out the right breast pump flange size for your body often takes a little experimenting.
In general, most people get the best results with a flange size that matches their measured nipple size exactly—but this isn’t a one-size-fits-all rule, and it really depends on what your specific nipples do during and after pumping.
For example, if you have elastic tissue and your nipples stretch significantly during pumping, you may need a flange size that’s 1-2mm smaller than your measured nipple size. As your nipples stretch, they also tend to get narrower, which means a smaller size might work better.
The smartest thing you can do is measure your nipples before you pump and after you pump, and then observe what happens while you are pumping, and then make yourself a fit kit by getting a few different sizes to try. Here is a general guide so you know where to get started:
Breast Pump Sizing Chart
To truly find your best fit, you’ll likely need to try a few different breast pump flange sizes to see which one feels most comfortable and allows you to collect the most milk in the shortest amount of time. I often recommend trying the size you measured, plus one size smaller and one size larger. So if you measure 17mm, experimenting with 16mm, 17mm, and 18mm flanges will give you a good "kit" to help you find the right size breast pump flange for your body.
Fitting Your Flanges
There are two different ways you can get your pump flanges to be the exact size you need—even if your breast pump didn’t come with them.
And remember: as long as your pump flange fit isn’t causing damage, there’s no right or wrong size or shape. You get to experiment to find what works best for you. If you’re planning to pump for a year (or more), taking the time to make sure you’ve got the right size pump flange is just as important as trying on shoes before running a marathon in them.
There are two good ways to get a smaller flange size, if you need it (and you probably do).
Replace Your Pump Flange
A few years ago, the variety of flange sizes was pretty limited. Now, you can easily find breast pump flanges in 1mm increments—ranging from 10mm all the way to 36mm.
And here’s the great news: you don’t need the same brand flange as your pump. Aftermarket flanges come in way more sizes and work just as well as the brand name options. Just make sure they’re compatible with your pump setup so the tubing and connectors fit correctly.
While this explosion of options has made it easier for people with different anatomy to get a better fit, it can feel overwhelming once you’ve figured out your flange size—because now you’re presented with shape options too.
Use Silicon Inserts
If you don’t love the idea of buying a bunch of different pump flanges, or you have a wearable pump where swapping flanges isn’t an option, silicone inserts are a great alternative. These can size down a standard 24mm flange to a smaller size.
My favorite silicone inserts are from a company called Lactation Hub. I love them because they’re thin and clear, which makes it easier to see your nipple through the sides—a huge help in making sure your pump flange fits well. They also offer assortments, so you can pick the exact flange sizes you want and build a custom fit kit just for you (and it's a small woman-owned business).
Checking Your Flange Fit
Once you’ve figured out your breast pump flange size and purchased the flanges you think will work best, it’s time to experiment. And this isn’t a step you want to rush through—if you really want to find your perfect fit, slow and steady is the way to go.
Think of this as a mini science experiment, and the prize? A comfortable pumping experience that helps you get the most milk with the least amount of effort.
You’ll need to test each of your flange sizes to find your ideal fit. In general, it’s best to use each flange for several days in a row to compare your output. Just one caveat: if you notice any discomfort or damage, stop using that size immediately.
A Correct Flange Fit
Here’s what you’re looking for in a correct flange fit:
- Comfortable – It shouldn’t hurt when you pump.
- Pulls just your nipple inside – Only your nipple should be moving in and out of the tunnel, not your areola. (Here’s a reel showing you exactly what this looks like: [Insert Reel Link].)
- Gives the most milk – You should see better milk output with less effort.
An Incorrect Flange Fit
Nipple damage can happen quickly, and it can be tricky to resolve once it starts. So, keep an eye on how your body feels, and monitor for early signs of damage. Taking pictures of your nipples before and after pumping is a great way to track any changes over time and catch potential issues early.
Signs your flange isn’t the right fit:
- It hurts – If it pinches or hurts, even with lubrication, it’s not the right size.
- You have rings on your areola – If you see circles or indentations where the flange pressed into your areola, your flange size is too big.
- You don’t feel emptied – If you still feel full after pumping, the flange size may not be right for you.
- You have to turn the vacuum up high – If you need to set your pump’s suction all the way up just to get milk out, that’s a sign your flange size isn’t working.
What to Do Next
Now that you understand how to measure your body, you’re all set to start making sure you have the right size breast pump flange. If you’re still pregnant, it’s totally fine to measure now—but just keep in mind your nipples may change after birth, especially if you have an epidural or are given IV fluids.
- Download the guide – or grab a flange ruler.
- Measure your nipples – using the guide or ruler.
- Test different flange sizes – Measure your nipples before and after pumping to see if they get bigger or stay the same size, then use the nipple sizing chart above to make a fit kit for yourself.
You can do this on your own, or many lactation consultants can help measure you during a consult and give you a recommendation about what to try first. But no matter where you start, think of the measurement (or recommendation) as your starting point. The real testing is where you try different flange sizes during different pump sessions to figure out what size feels best, fits best, and works best for your unique body.
Confidently Moving Forward
Getting the right size breast pump flange isn’t automatic, but when you find the size that fits exactly right for you, it’s an absolute game changer. Pumping is a lot of work—you deserve a pump flange fit that gives you the most payoff for all the effort you’re putting in.
Knowing you’ve found your right size flange might not make you love pumping (because let’s be honest—no one does), but it will give you that quiet confidence that comes with knowing you’re doing the exact right thing for your body. Not because someone told you, but because you tested it and saw the results yourself.
And like in any profession, when new research comes out, it can take time to trickle down to everyone. So if you ever work with a lactation consultant who suggests going up 2-5mm, don’t second guess yourself if you’ve already figured out what’s working best for you.
You know your body better than anyone else, and it’s always OK to trust yourself.
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